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Published on: June 19, 2012
SecB functions as a cytosolic signal recognition factor for protein export in E. coli
1Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, New York 10021.
Cell
|August 25, 1989
Summary
SecB protein is essential for preprotein translocation across E. coli membranes. This cytosolic protein competes with signal recognition particle (SRP) and is required for protein transport into inverted vesicles (INV).
Area of Science:
- Molecular Biology
- Cell Biology
- Protein Translocation
Background:
- Preprotein translocation across cellular membranes is a fundamental process.
- Signal recognition particle (SRP) is known to mediate protein targeting in eukaryotes.
- The mechanisms of protein translocation in prokaryotes are less understood.
Purpose of the Study:
- To investigate the role of the SecB protein in protein translocation in E. coli.
- To determine if SecB functions as a prokaryotic equivalent of SRP.
Main Methods:
- Purification of the SecB protein.
- Competition assays for signal sequence binding.
- Cell fractionation and immunoblot analysis.
- In vitro translocation assays using inverted vesicles (INV).
Main Results:
- Purified SecB tetramer binds to preprotein signal sequences.
- SecB competes with SRP for signal sequence binding.
- SecB is a cytosolic protein.
- E. coli depleted of SecB loses translocation activity, which is restored upon SecB readdition.
Conclusions:
- SecB is a crucial cytosolic factor for preprotein translocation in E. coli.
- SecB acts as a prokaryotic homolog of SRP, facilitating protein targeting to the membrane.
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